1. Field of the Invention
The invention relates to denture adhesives and to methods for making and using denture adhesives.
2. Description of Related Art
Ordinary removable dentures and dental plates function as a substitute for all or part of missing teeth ordinarily found in the mouth. While dentures are usually carefully fitted for the user, the fit can change over time, causing discomfort and slippage. In order to alleviate the discomfort and to control the slippage, a denture adhesive may be applied to the denture. The denture adhesive acts both as an adherent and as a gasket or cushion between the dentures and the gums of the denture wearer.
Denture adhesives are required to provide a diverse range of seemingly contradictory properties in an extraordinarily complex environment: the human mouth. Denture adhesives must develop a quick tack upon contact with the oral mucosa to prevent the denture from coming loose; they must also develop cohesive strength quickly when hydrated with moisture or saliva. They must also hold the denture in place for an indefinite period of time during use. They should only need to be applied once per day and should be nontoxic and organoleptically acceptable. They must not be easily washed out. But, denture adhesives must also easily release from the dentures and oral mucosa after use.
Several attempts have been made to fashion a denture adhesive using various polymer salts. One preferred polymer from the field is a copolymer of maleic anhydride and alkyl vinyl ether, sold under the Gantrez.RTM. trade name. This class of polymers was described as a possible denture adhesive in Germann et al. U.S. Pat. No. 3,003,988, which issued more than 30 years ago.
That patent describes synthetic, water sensitized but water insoluble, materials comprising mixed partial salts of lower alkyl vinyl ether--maleic anhydride copolymers for stabilizing dentures. The salts mentioned in the patent are a mixture of (a) calcium and (b) alkalies, including sodium, potassium and quaternary ammonium compounds in a 1:1 to 5:1 molar ratio. The calcium and alkali materials are added to the copolymer to form a mixed salt. The use of this class of materials has been described in a variety of other patents. Examples include U.S. Pat. Nos. 5,093,387, 5,037,924, 4,980,391 and 4,373,036, European Published Patent Application No. 406,643.
In order to provide additional adhesive and cohesive properties to denture adhesives made from Gantrez.RTM. polymers, one approach has been to manipulate the salt form of the copolymer. Examples can be found in WO 92/22280, WO 92/10988, WO 92/10987, and WO 92/10986.
One approach is found in U.S. Pat. No. 4,758,630 to Shah et al., issued Jul. 19, 1988. That patent is directed to denture adhesives having partial salts of zinc or strontium.
Another approach is reported in U.S. Pat. No. 5,073,604 to Holeva et al., issued Dec. 17, 1991. That patent is directed to a denture adhesive made from a partial salt of a Gantrez.RTM. polymer. The cations are zinc or strontium ions in combination with calcium, and optionally sodium, cations.
U.S. Pat. No. 5,298,534 to Prosise et al., issued Mar. 29, 1994 reports using Gantrez.RTM. salts of calcium, sodium, strontium, zinc, magnesium and potassium with boron cross-linked guar gum and an oil base as a carrier. The preferred mixed salt is a Ca/Na mixed salt. The guar gum is "critical" to claimed extended holding power and viscosity building properties.
Another approach has been to employ an adhesion adjuvant in the formulation or converting the copolymer into a terpolymer, and examples of these approaches can be found in U.S. Pat. No. 3,736,274, 5,037,924 and 5,093,387. Despite the efforts which have been put into improving the properties of maleic anhydride/alkyl vinyl ether type polymers and their salts, these formulations do not provide the full desired measure of adhesion, cohesion and resistance to washout from beneath the denture.